The invention relates to a static converter circuit having several static converters and having at least one transformer, the static-converter-side winding of which is effectively connected to the alternating-voltage connections of the static converter and the power-system-side winding of which is effectively connected to an alternating-current power system. The invention also relates to a method for controlling a static converter circuit.
The invention is based on the Swiss in-house journal "Brown Boveri Mitteilungen" 12 (1979), pages 763-777, as the closest prior art. According to this, it is known to feed converter locomotives with three-phase asynchronous motors from a 162/3-Hz railroad power system via a direct-voltage link circuit. In this arrangement, the direct voltage is obtained from the railroad power system by means of a current summing transformer which has several part windings with a common transformer core and by means of several four-quadrant actuators connected to these part windings. The four-quadrant actuators are operated in sub-harmonic mode and need a relatively large inductance on the alternating-current side which is obtained with the aid of a high short-circuit voltage of the transformer of about 30%. Such transformers are expensive and have high energy losses in the copper parts.
Circuit and operation of a four-quadrant actuator are described in the German journal "Elektrische Bahnen" 6 (1974), pages 135-142. This circuit allows an alternating-current power system to be connected to a direct-voltage link circuit (link circuit with impressed voltage). Two four-quadrant actuators which are connected in parallel on the power-system side via one secondary transformer winding, each operate into a common link circuit. Control is effected by phase-shifted pulsing of the two four-quadrant actuators at a frequency of about 11.162/3 Hz. As a result of this relatively high pulsing frequency, high energy losses are produced in the circuit components of the four-quadrant actuators.